Optical glass

ABSTRACT

The present invention provides an optical glass that has a high refractive index property and excels in a light transmittance property in the visible range and in resistance to devitrification. The optical glass contains from 3 to 18 mass % of SiO2, from 5 to 11.5 mass % of B2O3, from 0 to 7 mass % of Al2O3, from 0 to 11 mass % of CaO, 1 mass % or less of ZnO, from 7 to 20 mass % of TiO2, from 3 to 38 mass % of Nb2O5, from 27 to 49.8 mass % of La2O3, from 6 to 14 mass % of Gd2O3, from 0 to 5 mass % of Y2O3, less than 6 mass % of Ta2O5, and 0.6 mass % or less of WO3, with a ratio of B2O3/SiO2 being from 1 to 2.

TECHNICAL FIELD

The present invention relates to an optical glass used in an opticalelement such as a lens.

A glass material is used as an optical element such as a lens in awearable device, such as eyeglasses with a projector, an eyeglasses-typeor goggle-type display, a virtual reality or augmented reality displaydevice, and a virtual image display device. The glass material isrequired to have a high refractive index property from the perspectiveof achieving a wider angle image, higher levels of brightness andcontrast, and improvement in light guiding characteristics, and thelike. In addition, compact and wide-angle imaging glass lenses are usedin applications such as vehicle-mounted cameras and visual sensors forrobots (see, for example, Patent Document 1). Such imaging glass lensesalso require a high refractive index property.

CITATION LIST Patent Literature

-   Patent Document 1: JP 2015-74572 A

SUMMARY OF INVENTION Technical Problem

However, typically, when a glass composition is blended for achieving ahigh refractive index, an element with light absorption in the visiblerange is often used as a component that increases the refractive index.Therefore, in general, a problem of high refractive index glass is thatthe light transmittance in the visible range is low. In addition, when aglass composition is blended for achieving a high refractive index, theamount of components constituting the glass skeleton tends to decrease.Therefore, in general, a problem of high refractive index glass is thatthe glass easily devitrifies and is inferior in terms of massproductivity.

In light of the foregoing, an object of the present invention is toprovide an optical glass having a high refractive index property andexcelling in a light transmittance property in the visible range and inresistance to devitrification.

Solution to Problem

As a result of diligent research by the present inventors, the presentinventors discovered that the problems described above can be solved byinclusion of high refractive index components such as TiO₂, Nb₂O₅,La₂O₃, and Gd₂O₃, and strict regulation of the contents of SiO₂ and B₂O₃that contribute to vitrification stability.

That is, the optical glass of the present invention contains from 3 to18 mass % of SiO₂, from 5 to 11.5 mass % of B₂O₃, from 0 to 7 mass % ofAl₂O₃, from 0 to 11 mass % of CaO, 1 mass % or less of ZnO, from 7 to 20mass % of TiO₂, from 3 to 38 mass % of Nb₂O₅, from 27 to 49.8 mass % ofLa₂O₃, from 6 to 14 mass % of Gd₂O₃, from 0 to 5 mass % of Y₂O₃, lessthan 6 mass % of Ta₂O₅, and 0.6 mass % or less of WO₃, with a ratio ofB₂O₃/SiO₂ being from 1 to 2.

The optical glass of the present invention preferably contains 36 mass %or greater of Ln₂O₃ (where Ln is at least one element selected from La,Gd, Y, and Yb).

The optical glass of the present invention preferably contains 0 mass %or greater but less than 0.2 mass % of BaO.

The optical glass of the present invention preferably has a refractiveindex (nd) of from 1.84 to 2.04.

The optical glass of the present invention preferably has a liquidustemperature of not higher than 1150° C.

The optical glass of the present invention preferably has a lineartransmittance of 72% or greater at a wavelength of 500 nm and athickness of 5 mm.

An optical element of the present invention includes the optical glassdescribed above.

Advantageous Effects of Invention

According to the present invention, an optical glass having a highrefractive index property and excelling in a light transmittanceproperty in the visible range and in resistance to devitrification canbe provided.

DESCRIPTION OF EMBODIMENTS

The optical glass according to an embodiment of the present inventioncontains from 3 to 18 mass % of SiO₂, from 5 to 11.5 mass % of B₂O₃,from 0 to 7 mass % of Al₂O₃, from 0 to 11 mass % of CaO, 1 mass % orless of ZnO, from 7 to 20 mass % of TiO₂, from 3 to 38 mass % of Nb₂O₅,from 27 to 49.8 mass % of La₂O₃, from 6 to 14 mass % of Gd₂O₃, from 0 to5 mass % of Y₂O₃, less than 6 mass % of Ta₂O₅, and 0.6 mass % or less ofWO₃, with a ratio of B₂O₃/SiO₂ being from 1 to 2. The reason forlimiting the glass composition in this manner is described below. Notethat, in the description regarding the content of each component below,“%” means “mass %” unless otherwise indicated.

SiO₂ is a glass skeletal component that improves vitrification stabilityand chemical durability. The content of SiO₂ is from 3 to 18%,preferably from 3.5 to 15%, more preferably from 4 to 12%, andparticularly preferably from 5 to 10%. When the content of SiO₂ is toolow, the effects described above are not easily achieved. On the otherhand, when the content of SiO₂ is too high, the refractive index tendsto decrease.

B₂O₃ is a component that contributes to vitrification stability. Thecontent of B₂O₃ is from 5 to 11.5%, preferably from 6.5 to 11.5%, morepreferably from 7 to 11%, even more preferably from 8 to 10.5%, andparticularly preferably 9% or greater but less than 10.5%. When thecontent of B₂O₃ is too low, the effects described above are not easilyachieved. On the other hand, when the content of B₂O₃ is too high, therefractive index tends to decrease, and chemical durability tends todecline.

Note that preferably, the proportions of SiO₂ and B₂O₃ are appropriatelyadjusted in order to increase vitrification stability and improve massproductivity. Specifically, a mass ratio of B₂O₃/SiO₂ is preferably from1 to 2, more preferably from 1.3 to 1.99, and particularly preferablyfrom 1.5 to 1.98. Note that in the present specification, “X/Y” means avalue obtained by dividing the content of X by the content of Y.

Al₂O₃ is a component that improves water resistance. However, when thecontent thereof is too high, the glass tends to easily devitrify.Therefore, the content of Al₂O₃ is from 0 to 7%, preferably from 0 to5%, more preferably from 0 to 2%, and particularly preferably from 0 to1%.

CaO is a component that readily contributes to particularlyvitrification stability, even amongst alkaline earth metal oxides.However, when the content thereof is too high, the refractive indextends to decrease. Therefore, the content of CaO is from 0 to 11%,preferably from 0.1 to 9%, more preferably from 1 to 8%, even morepreferably from 2 to 7%, and particularly preferably from 3 to 6%.

ZnO is a component that promotes devitrification in the compositionsystem according to an embodiment of the present invention, and thus thecontent thereof is preferably low. Specifically, the content of ZnO is1% or less, preferably 0.5% or less, and even more preferably 0.1% orless, and particularly preferably, ZnO is not contained.

TiO₂ is a component that increases the refractive index of glass. TiO₂also has an effect of improving chemical durability. The content of TiO₂is from 7 to 20%, preferably from 8 to 18%, more preferably from 9 to17%, and particularly preferably from 10 to 16%. When the content ofTiO₂ is too low, the effects described above are not easily achieved. Onthe other hand, when the content of TiO₂ is too high, the transmittanceof the glass in the visible range tends to decrease, and thevitrification stability tends to decline.

Nb₂O₅ is a component that increases the refractive index of glass. Thecontent of Nb₂O₅ is from 3 to 38%, preferably from 4 to 30%, morepreferably from 5 to 19%, even more preferably from 6 to 14%, andparticularly preferably from 7 to 10%. When the content of Nb₂O₅ is toolow, the above effect is not easily achieved. On the other hand, whenthe content of the Nb₂O₅ is too high, the resistance to devitrificationdeclines, and mass productivity tends to decrease. In addition, lighttransmittance in the visible range tends to decrease.

La₂O₃ is a component that increases the refractive index and alsoimproves vitrification stability. The content of La₂O₃ is from 27 to49.8%, preferably from 30 to 49.5%, more preferably from 35 to 49%, andparticularly preferably from 38 to 48.5%. When the content of La₂O₃ istoo low, the effects described above are not easily achieved. On theother hand, when the content of La₂O₃ is too high, devitrificationeasily occurs. Decrease in the resistance to devitrification tends tolead to deterioration in mass productivity.

Gd₂O₃ is also a component that increases the refractive index andimproves vitrification stability. The content of Gd₂O₃ is from 6 to 14%,preferably from 6 to 10%, and particularly preferably from 6 to 9%.

Y₂O₃ is a component that improves vitrification stability withoutreducing the refractive index. However, when the content is too high,devitrification and striae easily occur. Thus, the content of Y₂O₃ isfrom 0 to 5%, preferably from 0.1 to 4%, more preferably from 0.3 to 2%,even more preferably from 0.4 to 1%, and particularly preferably from0.5 to 0.8%.

Ta₂O₅ is a component that increases the refractive index. However, whenthe content thereof is too high, phase separation and devitrificationeasily occur. Also, since Ta₂O₅ is a rare and expensive component, asthe content thereof increases, the batch cost of the raw material alsoincreases. In view of the foregoing, the content of Ta₂O₅ is less than6%, preferably 3% or less, and more preferably 1% or less, andparticularly preferably, Ta₂O₅ is not contained.

WO₃ is a component that increases the refractive index, but tends toreduce light transmittance in the visible range. Therefore, the contentthereof is 0.6% or less, preferably 0.5% or less, and more preferably0.3% or less, and particularly preferably, WO₃ is not contained.

The optical glass according to an embodiment of the present inventionmay contain the following components in addition to the componentsdescribed above.

Yb₂O₃ is a component that increases the refractive index. However, whenthe content thereof is too high, devitrification and striae easilyoccur. Thus, the content of Yb₂O₃ is from 0 to 10%, and preferably from0 to 8%.

ZrO₂ is a component that increases the refractive index and chemicaldurability. The content of ZrO₂ is from 0 to 10%, preferably from 1 to9%, more preferably from 3 to 8%, even more preferably from 4 to 7.5%,and particularly preferably from 5 to 7%. When the content of ZrO₂ istoo high, devitrification easily occurs.

SrO is a component that contributes to vitrification stability. However,when the content thereof is too high, the refractive index tends todecrease. Therefore, the content of SrO is from 0 to 11%, preferablyfrom 0.1 to 9%, and particularly preferably from 1 to 8%.

BaO is a component that contributes to vitrification stability andincreases the refractive index. However, when BaO is included, thedensity of the glass increases, and a weight of an optical elementincluding the optical glass according to an embodiment of the presentinvention tends to increase. Therefore, inclusion of BaO is notparticularly preferable for applications such as wearable devices.Accordingly, the content of BaO is 1% or less, preferably 0.5% or less,and more preferably 0.2% or less, and particularly preferably, BaO isnot included.

Li₂O, Na₂O, and K₂O are components that reduce the softening point, butwhen the contents thereof are too high, devitrification easily occurs.Therefore, the content of each of these components is from 0 to 3%, andpreferably from 0 to 1%, and particularly preferably, these componentsare not included.

The content of Ln₂O₃ is preferably 36% or greater, 40% or greater, or45% or greater, and particularly preferably 48% or greater. Therefractive index and light transmittance in the visible range can beincreased by setting the content thereof to such a level. The upperlimit of the content of Ln₂O₃ is not particularly limited, but when thecontent is too high, devitrification easily occurs. Therefore, the upperlimit is preferably not greater than 70%, or not greater than 65%, andis particularly preferably not greater than 60%. Note that in Ln₂O₃, Lnis at least one element selected from La, Gd, Y, and Yb. That is, thecontent of Ln₂O₃ denotes the total amount of La₂O₃, Gd₂O₃, Y₂O₃, andYb₂O₃.

In order to obtain glass having a high refractive index and excelling invitrification stability in the present invention, preferably, a ratio ofthe total amount of SiO₂ and B₂O₃ to the amount of Ln₂O₃ isappropriately adjusted. Specifically, the ratio of (SiO₂+B₂O₃)/Ln₂O₃ ispreferably from 0.15 to 0.9, more preferably from 0.2 to 0.6, andparticularly preferably from 0.25 to 0.5. Note that “X+Y+ . . . ” hereinrefers to a total amount of the components.

In the present invention, it is preferable to appropriately adjustproportions of Nb₂O₅, TiO₂, and WO₃ in order to obtain glass that has ahigh refractive index and excels in transmittance in the visible range.Specifically, a mass ratio of Nb₂O₅/(Nb₂O₅+TiO₂+WO₃) is preferably from0.15 to 0.8, more preferably from 0.2 to 0.6, and particularlypreferably from 0.3 to 0.5.

In order to obtain glass that has a high refractive index and excels intransmittance in the visible range, it is preferable to appropriatelyadjust a ratio of TiO₂ to Nb₂O₅. Specifically, the mass ratio ofTiO₂/Nb₂O₅ is preferably 0.3 or greater, more preferably 0.5 or greater,even more preferably 0.8 or greater, and is particularly preferably 1 orgreater. When the mass ratio above is too small, the effects describedabove are not easily obtained. In addition, vitrification tends to beunstable.

In the present invention, it is preferable to appropriately adjust atotal amount of TiO₂, WO₃, and Nb₂O₅ in order to obtain glass excellingin transmittance in the visible range. Specifically, the total amount ofTiO₂+WO₃+Nb₂O₅ is preferably 45% or less, more preferably 30% or less,even more preferably 27% or less, and particularly preferably 25% orless.

In the present invention, in order to increase the refractive index andlight transmittance in the visible range and to improve vitrificationstability, preferably, a ratio of Y₂O₃ to Ln₂O₃ is appropriatelyadjusted. Specifically, the ratio of Y₂O₃/Ln₂O₃ is preferably from 0 to0.1 or from 0.005 to 0.05, and is particularly preferably from 0.01 to0.3.

In the present invention, in order to increase the refractive index andlight transmittance in the visible range, and to improve vitrificationstability, preferably, a ratio of Gd₂O₃ to Ln₂O₃ is appropriatelyadjusted. Specifically, the ratio of Gd₂O₃/Ln₂O₃ is preferably from 0.1to 0.25, and particularly preferably from 0.12 to 0.2.

In the present invention, preferably, proportions of Nb₂O₅, TiO₂, ZrO₂,WO₃, and Ln₂O₃ are appropriately adjusted in order to obtain glass thathas a high refractive index and excels in transmittance in the visiblerange. Specifically, a mass ratio of Nb₂O₅/(Nb₂O₅+TiO₂+ZrO₂) ispreferably from 0.1 to 0.46, more preferably from 0.15 to 0.4, andparticularly preferably from 0.2 to 0.37.

In the present invention, in order to increase the refractive index andlight transmittance in the visible range and to improve vitrificationstability, it is preferable to appropriately adjust a ratio of a totalamount of TiO₂ and B₂O₃ to a total amount of WO₃ and Nb₂O₅.Specifically, the ratio of (TiO₂+B₂O₃)/(WO₃+Nb₂O₅) is preferably from1.6 to 4, and particularly preferably from 2 to 3.5.

In the present invention, in order to increase vitrification stability,it is preferable to appropriately adjust a ratio of a total amount ofCaO, SrO, BaO, and ZnO to a total amount of Nb₂O₅, La₂O₃, TiO₂, andZrO₂. Specifically, the ratio of(CaO+SrO+BaO+ZnO)/(TiO₂+Nb₂O₅+La₂O₃+ZrO₂) is preferably from 0 to 0.6,more preferably from 0.01 to 0.4, and particularly preferably from 0.03to 0.3.

Note that the environmental load of As components (As₂O₃, and the like)and Pb components (PbO, and the like) is large, and thus thesecomponents are preferably not included.

The refractive index (nd) of the optical glass according to anembodiment of the present invention is preferably from 1.84 to 2.04,more preferably from 1.88 to 2.01, and particularly preferably from 1.89to 2.00. In addition, at a wavelength of 500 nm and a thickness of 5 mm,the light transmittance (linear transmittance) in the visible range ofthe optical glass according to an embodiment of the present invention ispreferably 72% or higher, more preferably 74% or higher, and even morepreferably 75% or higher. When the optical characteristics describedabove are satisfied, the optical glass according to an embodiment of thepresent invention is suitable as an optical element such as an imagingglass lens that is compact and can capture images with a wide range.

Note that an Abbe number (νd) of the optical glass according to anembodiment of the present invention is not particularly limited, but inconsideration of vitrification stability, the Abbe number (νd) ispreferably not greater than 39, preferably not greater than 35,particularly preferably not greater than 31, and further preferably notgreater than 30.

A partial dispersion ratio (θg, F) of the optical glass according to anembodiment of the present invention is preferably 0.615 or less,preferably 0.61 or less, and particularly preferably 0.6 or less. Whenthe partial dispersion ratio is too large, chromatic aberration easilyoccur.

A liquidus temperature of the optical glass according to an embodimentof the present invention is preferably 1150° C. or lower, preferably1100° C. or lower, and particularly preferably 1070° C. or lower. Whenthe liquidus temperature is set to such a temperature, mass productivityis readily improved because devitrification does not easily occur duringmelting or forming.

EXAMPLES

The present invention is described in detail below using examples, butthe present invention is not limited to these examples.

Tables 1 and 2 show examples (No. 1 to 10) of the present invention.

TABLE 1 (mass %) 1 2 3 4 5 6 SiO₂ 5.3 7.21 9.21 5.73 5.54 5.8 Al₂O₃ B₂O₃10.0 10.26 10.26 11.29 10.9 11.4 CaO 4.11 4.4 SrO 7.34 BaO ZnO TiO₂14.49 11.93 10.0 13.12 12.68 13.25 Nb₂O₅ 8.1 8.15 7.4 8.97 8.67 7.9 ZrO₂5.87 5.91 5.91 6.51 6.29 6.6 La₂O₃ 47.9 48.2 48.87 41.1 39.72 41.5 Gd₂O₃7.7 7.7 7.73 8.51 8.22 8.6 Y₂O₃ 0.6 0.6 0.6 0.66 0.64 0.65 Yb₂O₃ Ta₂O₅WO₃ Ln₂O₃ 56.2 56.5 57.2 50.3 48.6 50.8 B₂O₃/SiO₂ 1.89 1.42 1.11 1.971.97 1.97 (SiO₂ + B₂O₃)/Ln₂O₃ 0.27 0.31 0.34 0.34 0.34 0.34Nb₂O₅/(Nb₂O₅ + 0.28 0.31 0.32 0.31 0.31 0.28 TiO₂ + ZrO₂) TiO₂/Nb₂O₅1.79 1.46 1.35 1.46 1.46 1.68 TiO₂ + WO₃ + Nb₂O₅ 22.6 20.1 17.4 22.121.4 21.2 Y₂O₃/Ln₂O₃ 0.011 0.011 0.010 0.013 0.013 0.013 Gd₂O₃/Ln₂O₃0.14 0.14 0.14 0.17 0.17 0.17 Nb₂O₅/(Nb₂O₅ + 0.36 0.41 0.43 0.41 0.410.37 TiO₂ + WO₃) (TiO₂ + B₂O₃)/(WO₃ + 3.02 2.72 2.74 2.72 2.72 3.12Nb₂O₅) (CaO + SrO + BaO + 0.00 0.00 0.00 0.06 0.11 0.06 ZnO)/(TiO₂ +Nb₂O₅ + La₂O₃ + ZrO₂) Refractive index nd 1.977 1.952 1.912 1.945 1.9401.935 Abbe number νd 28.4 30.7 31.2 29.9 30.0 29.9 Partial dispersion0.601 0.595 0.610 0.598 0.598 0.597 ratio θ g, F Liquidus temperature1120 1100 1140 1050 1090 1060 (° C.) Linear transmittance 76 77 78 77 7777 (%)

TABLE 2 (mass %) 7 8 9 10 SiO₂ 6.5 6.5 6.3 5.55 Al₂O₃ B₂O₃ 8.26 9.42 7.18.09 CaO SrO BaO ZnO TiO₂ 14.43 14.91 13.4 14.13 Nb₂O₅ 7.36 5.75 7.17.21 ZrO₂ 5.85 5.92 5.6 5.73 La₂O₃ 47.7 48.47 48.1 46.9 Gd₂O₃ 7.7 7.357.4 7.4 Y₂O₃ 2.2 1.7 5.0 5.0 Yb₂O₃ Ta₂O₅ WO₃ Ln₂O₃ 57.6 57.5 60.5 59.3B₂O₃/SiO₂ 1.27 1.45 1.13 1.46 (SiO₂ + B₂O₃)/Ln₂O₃ 0.26 0.28 0.22 0.23Nb₂O₅/(Nb₂O₅ + 0.27 0.22 0.27 0.27 TiO₂ + ZrO₂) TiO₂/Nb₂O₅ 1.96 2.591.89 1.96 TiO₂ + WO₃ + Nb₂O₅ 21.8 20.7 20.5 21.3 Y₂O₃/Ln₂O₃ 0.038 0.0300.083 0.084 Gd₂O₃/Ln₂O₃ 0.13 0.13 0.12 0.12 Nb₂O₅/(Nb₂O₅ + 0.34 0.280.35 0.34 TiO₂ + WO₃) (TiO₂ + B₂O₃)/(WO₃ + 3.08 4.23 2.89 3.08 Nb₂O₅)(CaO + SrO + BaO + 0.00 0.00 0.00 0.00 ZnO)/(TiO₂ + Nb₂O₅ + La₂O₃ +ZrO₂) Refractive index nd 1.998 1.985 2.000 2.004 Abbe number νd 29.029.4 29.0 28.9 Partial dispersion — — — 0.600 ratio θg, F Liquidustemperature 1130 1150 1150 1150 (° C.) Linear transmittance 78 73 73 77(%)

First, glass raw materials were blended to prepare each of thecompositions shown in Tables 1 and 2, and were melted at a temperaturefrom 1200 to 1350° C. for 2 hours using a platinum crucible. The moltenglass was poured onto a carbon plate and annealed by maintaining it at700 to 800° C. for 2 to 72 hours, and thereby samples suitable for eachmeasurement were produced.

The refractive index (nd), Abbe number (νd), light transmittance, andliquidus temperature were measured for the produced samples. The resultsare shown in Tables 1 and 2.

The refractive index was presented as a measured value for a d-line(587.6 nm) of a helium lamp.

The Abbe number was calculated from the equation of Abbe number(νd)=[(nd−1)/(nF−nC)] using the above-mentioned refractive index ford-line, a refractive index value for an F-line (486.1 nm) of a hydrogenlamp, and a refractive index value for a C-line (656.3 nm) of thehydrogen lamp.

The liquidus temperature was measured by remelting the glass in anelectric furnace at 1200° C. for 0.5 hours, holding the material for 18hours in an electric furnace having a temperature gradient. And then thematerial was removed from the electric furnace, and cooled in air. Theglass was observed using an optical microscope and a precipitationposition of a devitrified substance was thus determined.

The linear transmittance was measured as follows. The lineartransmittance including surface reflection loss of an optically polishedsample having a thickness of 5 mm±0.1 mm was measured at 0.5 nmintervals using a spectrophotometer (UV-3100, available from ShimadzuCorporation). The linear transmittance at a wavelength of 500 nm wasread from a light transmittance curve obtained through the measurements.

As shown in Tables 1 and 2, the samples of Examples No. 1 to 10exhibited the desired optical characteristics, had a low liquidustemperature of 1150° C. or lower, and excelled in resistance todevitrification. In addition, the linear transmittance at a wavelengthof 500 nm was 73% or higher, which was excellent.

1. An optical glass comprising from 3 to 18 mass % of SiO₂, from 5 to11.5 mass % of B₂O₃, from 0 to 7 mass % of Al₂O₃, from 0 to 11 mass % ofCaO, 1 mass % or less of ZnO, from 7 to 20 mass % of TiO₂, from 3 to 38mass % of Nb₂O₅, from 27 to 49.8 mass % of La₂O₃, from 6 to 14 mass % ofGd₂O₃, from 0 to 5 mass % of Y₂O₃, less than 6 mass % of Ta₂O₅, and 0.6mass % or less of WO₃, with a ratio of B₂O₃/SiO₂ being from 1 to
 2. 2.The optical glass according to claim 1, further comprising 36 mass % orgreater of Ln₂O₃, where Ln is at least one element selected from La, Gd,Y, and Yb.
 3. The optical glass according to claim 1, further comprising0 mass % or greater but less than 0.2 mass % of BaO.
 4. The opticalglass according to claim 1, wherein a refractive index (nd) is from 1.84to 2.04.
 5. The optical glass according to claim 1, wherein a liquidustemperature is not higher than 1150° C.
 6. The optical glass accordingto claim 1, wherein a linear transmittance at a wavelength of 500 nm anda thickness of 5 mm is 72% or greater.
 7. An optical element comprisingthe optical glass described in claim
 1. 8. The optical glass accordingto claim 2, further comprising 0 mass % or greater but less than 0.2mass % of BaO.
 9. The optical glass according to claim 2, wherein arefractive index (nd) is from 1.84 to 2.04.
 10. The optical glassaccording to claim 3, wherein a refractive index (nd) is from 1.84 to2.04.
 11. The optical glass according to claim 8, wherein a refractiveindex (nd) is from 1.84 to 2.04.
 12. The optical glass according toclaim 2, wherein a liquidus temperature is not higher than 1150° C. 13.The optical glass according to claim 3, wherein a liquidus temperatureis not higher than 1150° C.
 14. The optical glass according to claim 4,wherein a liquidus temperature is not higher than 1150° C.
 15. Theoptical glass according to claim 8, wherein a liquidus temperature isnot higher than 1150° C.
 16. The optical glass according to claim 9,wherein a liquidus temperature is not higher than 1150° C.
 17. Theoptical glass according to claim 10, wherein a liquidus temperature isnot higher than 1150° C.
 18. The optical glass according to claim 11,wherein a liquidus temperature is not higher than 1150° C.
 19. Theoptical glass according to claim 2, wherein a linear transmittance at awavelength of 500 nm and a thickness of 5 mm is 72% or greater.
 20. Theoptical glass according to claim 3, wherein a linear transmittance at awavelength of 500 nm and a thickness of 5 mm is 72% or greater.